As is well known, it has been desirable to operate the engine close to the engine's surge line in order to achieve transients as fast as possible. Obviously, excursions beyond the surge line cannot be tolerated inasmuch as surge can result in catastropic conditions. Typically, engine controls for gas turbine engines have built-in safety measures to prevent the engine from going into surge. These controls would generally monitor certain engine parameters and by an open-looped schedule account for the surge characteristics of the particular engine for which it was designed.
Also well known is that the industry has seen attemps to take advantage of opening the compressor bleeds during transient conditions to achieve a faster response and operate closer to the surge line. An example of such a system is disclosed in U.S. Pat. No. 3,006,145 granted to A. J. Sobey on Oct. 31, 1961. However, in such a control mode it is exceedingly important to be able to ascertain when a given rate has been exceeded which is not attainable by the prior art controls as disclosed in the above-noted patent.